elements

Introduction

Fluorine (elemental symbol: F) is the lightest and most reactive of the halogen elemental class. While many sources state that fluorine is too reactive to be found naturally, that’s not exactly true since small amounts of fluorine gas can be found trapped in some violet crystals of the mineral fluorite.

Until the Atomic Age there was no large-scale production of fluorine gas (F2). But large quantities of fluorine were needed to isolate the isotopes of uranium (U) from gaseous UF6 . Today, fluorine gas is available commercially in pressurized cylinders and is handled with the utmost care. In modern laboratories chemists take care to avoid any accidental production of fluorine gas. But the story of the first laboratory production of fluorine gas highlights the excitement and risks inherent in scientific discovery.

Hints and Suspicions

In 1530 Georgius Agricola describes a mineral he called fluorspar after the Latin fluere (to flow) which had use as a flux to help the flow-ability of molten metals. Fluorspar, also known as fluorite, we now know contains calcium fluoride (CaF2) and large deposits are widely distributed around the world.

In 1670 Heinrich Schwanhard was the first to report that a mixture of fluorite and acid produced a gas that was useful in etching glass. This process led to decorative frosted glasses. The etching agent was later identified in 1771 by Carl Scheele , a pharmacist, as hydrofluoric acid (HF). Scheele is credited with the first discovery of oxygen, citric acid, hydrogen cyanide and other chemicals in addition to hydrofluoric acid. After Scheele’s work on hydrofluoric acid, the hunt was on in earnest for fluorine. At the time there were already successful attempts in isolating the related element chlorine from chloride salts and hydrochloric acid by electrolysis (Both Humphrey Davy and Scheele achieved this.) By the 1810‘s many suspected that a new element (fluorine), similar to chlorine but probably more reactive, was present in hydrofluoric acid.

The Dangerous Endeavor

While “Scientists learn more from their failures than their successes.” is a common saying, this is true only if you survive the failures. Although, other scientists would learn not to repeat your fatal mistake.

The quest for fluorine was going to take a toll on health and lives. In hindsight, you might want to have known:

that fluorine reacts with nearly every element,

that fluorine and hydrogen fluoride (HF) are very damaging to soft tissue (killing the cells, penetrating to and reacting with bones),

that hydrogen fluoride causes damage to respiratory tracks even in small amounts,

that fluorine and hydrogen react with each other explosively,

that “fluorine fires” are usually unquenchable and

that fluorine can react with heavy metals to form poisonous gases.

But at the time, none of these were known, although some of these properties were suspected based on the observed effects of chlorine and hydrogen chloride. The scientists did take reasonable precautions, however, the power of fluorine was surprisingly dangerous.

1813: Sir Humphrey Davy fails to isolate fluorine via electrolysis of fluoride salts. He experienced damage to his eyes and fingernails from HF but recovers. He accurately predicts some of the properties of fluorine.

Jerome Nickles also dies from HF exposure while working on electrolysis.

1836: George and Thomas Knox used an apparatus constructed from fluorspar (since fluorine seemed to react with everything else) to heat fluoride salts of mercury in a chlorine atmosphere. Thomas was nearly killed and George was bed-ridden for three years from HF exposure.

1856: Edmund Fremy was the first to prepare potassium bifluoride (KHF2) and used it to isolate and identify hydrogen fluoride (HF), the mysterious gas that was making fluorine investigations so dangerous. He attempts the electrolysis of fused potassium fluoride (KF) – possibly producing some fluorine gas, but was unable to isolate any of the very reactive gas.

1886: Henri Moissan successfully isolates fluorine gas in a platinum vessel via electrolysis of anhydrous (water-free) hydrogen fluoride plus potassium bifluoride at -23° Celsius. Following this success, he continued his work determining the properties of fluorine. In his experiments Moissan was poisoned several times.

Apparatus for isolating fluorine

Henri Moissan

In 1906, Henri Moissan won a Nobel Prize for his work on the isolation of fluorine, a feat that had eluded scientists for 75 years. He also famously pioneered work with high temperature furnaces, creating many previously unknown compounds. He died suddenly (after surgery for an appendicitis) in early 1907 shortly after returning from the Nobel Prize ceremony.